This
is our seventh Case of the Week. These cases can also be accessed by clicking
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This
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This
case was contributed by Dr. Peter Morawiecki, Great LakesNavalHospital, Great Lakes,
Illinois (USA). We invite you to contribute a Case of the Week by sending an
email to [email protected]with microscopic images in JPG or GIF format, with a clinical history and
any other images (gross, immunostains, EM, etc.) that may be helpful. We particularly
need cases of GI, GU and Gynecologic pathology. Please only send cases with a
definitive diagnosis.

Case
of the Week #7

A 19 year
old man had a few month history of a 0.5 cm subcutaneous, firm, grey lump on
the right wrist. It was clinically suspected to be an epidermal cyst.

Blue
nevi appear to arise from the arrested migration of immature melanocytes in the
dermis. They are uncommon, and are usually diagnosed in adults, but may become
apparent in early childhood or even at birth. Their blue color (clinically) is
due to the Tyndall effect of selective absorption of parts of the light
spectrum by deeply located (dermal) melanin pigment, which is usually
abundant. There are several types of blue nevi, including common, cellular,
atypical cellular, epithelioid and malignant.

The
cellular blue nevus most commonly involves the buttock and sacrococcygeal
areas, but may also involve the scalp, face, hands and feet. It is considered
benign, but may rarely recur or involve regional lymph nodes. Unfortunately,
no specific features to date have been identified to indicate whether cellular
blue nevi will have aggressive behavior.

Cellular
blue nevi are usually large (greater than 1.5 cm), with intense pigmentation.
Microscopically, they consist of a well circumscribed collection of
interweaving fascicles with increased cellularity and infiltration into the
subcutaneous tissue. Heavily pigmented spindle and dendritic cells alternate
with clear cells. The cells have finely eosinophilic or clear cytoplasm, with
vesicular nuclei and small nucleoli. They may rarely be amelanotic. The
margins are usually pushing. There is no/minimal atypia, no nuclear
pleomorphism, no epidermal invasion, no peripheral inflammation, no necrosis
and no/minimal mitotic figures. However, scalp lesions may exhibit
intracranial extension.

Cellular
blue nevi, as well as common blue nevi, are immunoreactive for melanocytic
stains, such as S100, HMB45 and MelanA/Mart1. Treatment consists of simple
excision.

The
differential diagnosis includes atypical cellular blue nevi, which exhibit
either atypia insufficient for a diagnosis of malignancy or a mitotic rate of
less than 2 per square millimeter. They are also treated with conservative
excision. The differential diagnosis may also include malignant blue nevi,
which are very rare melanomas that are highly aggressive and may metastasize
and cause death. They either have malignant cytology with a benign blue nevi
component, or appear benign at low power but have infiltrative borders,
necrosis, mitotic figures or atypia at higher power.